Question

The pair of lanthanides with the highest third ionization energy is

• A. $Lu$ and $Yb$
• B. $Eu$ and $Gd$
• C. $Eu$ and $Yb$
• D. $Dy$ and $Yb$

Answer 1

Answer: (C)

$Eu=\left[Xe\right]4f^{1}5d^{0}6s^2$ and $Yb=\left[Xe\right]4f^{14}5d^{0}6s^2$ Removal of $3^{rd}$ electron requires more energy from these elements.